What’s the deal with DMDM hydantoin — and why is TikTok so damn concerned about it?

If you want to spread a message far and wide with just the click of a button, TikTok is the place to share it. That’s what happened earlier this year, when a user — and then another, and another — caught wind of class action lawsuits alleging that a haircare ingredient called DMDM hydantoin causes scalp irritation and hair loss. 

Suddenly, the platform was buzzing with videos of users making similar claims and warning others to avoid products with DMDM. (Today, videos tagged with #dmdm have collected more than 37 million views.)

Here’s what we know about DMDM hydantoin, so far:

What is DMDM hydantoin?

We’ll unpack those claims in a minute, but in the meantime, let’s break down the ingredient in question. “DMDM hydantoin is a preservative used to protect cosmetics from microbial spoilage throughout their shelf life,” says cosmetic chemist Kelly Dobos. 

Preservatives work in a myriad of different ways, but DMDM hydantoin is part of a class referred to as formaldehyde releasers because they do just that: release “very small amounts of formaldehyde over the lifetime of [a] product,” according to Dobos. 

Is DMDM hydantoin safe?

If that sounds off-putting, consider that formaldehyde occurs naturally in foods like bananas, carrots, and apples. In fact, the amount of formaldehyde released by DMDM hydantoin is roughly equivalent to that of a pear. 

“The Cosmetic Ingredient Review (CIR) panel of expert physicians and toxicologists concluded that free formaldehyde in cosmetics should not exceed 0.2%,” reports Dobos. “DMDM hydantoin is typically used at concentrations of less than half a percent total, which means it’s unlikely cosmetics contain levels above that recommendation.”

Nevertheless, TikTok users heard the words “formaldehyde” and “hair loss” and ran with them — to the point that major beauty brands like Tresemmé and OGX (the parent companies of which were cited in the aforementioned lawsuits) actively removed DMDM hydantoin from their formulas and took to their websites to directly address said claims.

A representative for Unilever-owned Tresemmé provided the following statement: “Though DMDM has been proven safe and is widely used in the beauty industry as a preservative, Tresemmé no longer uses DMDM in our product formulations.”

A statement provided by OGX, a subsidiary of Johnson & Johnson, had a similar sentiment: “Our new product launches do not contain the preservative DMDM Hydantoin. In fact, we haven’t launched any new hair care products with this ingredient in the last several years. 

“Some of our existing products contain a small amount of DMDM Hydantoin. Every preservative used in our products must clear our rigorous safety assessment process. We also offer a range of formulas with a variety of different preservatives that meet evolving consumer ingredient preferences.”

The bottom line is this: while DMDM hydantoin does release trace amounts of formaldehyde, there’s no scientific evidence it can make your hair fall out. “If it really was the cause of hair loss the industry would have stopped using it long ago,” says Dobos.